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Chapter 18Evolution of Plants and
Fungi
The Evolution of Plants Spans 500 Million Years
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18.1 Evidence suggests that plants evolved from green algae Plants - multicellular, photosynthetic eukaryotes
that range in size from the duckweed to the giant coastal redwoods Important ecologically, industrially, and medically
Believed to have evolved from freshwater green algae over 500 million years ago Evidence - Both green algae and plants
Contain chlorophylls a and b and various accessory pigments
Store excess carbohydrates as starch Have cellulose in their cell wall
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Figure 18.1 Close algal relatives of plants
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18.2 The evolution of plants is marked by four innovations
Nourish and protect a multicellular embryo that completes the life cycle
Have vascular tissue transporting water and solute to cells when the plant body is surrounded by air
Produce seeds that contain an embryo and stored organic nutrients within a protective coat
Flowers that attract pollinators, such as insects, and give rise to fruits, food for animals to help disperse the seeds
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Figure 18.2A Representatives of the four major groups of plants
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Figure 18.2B Evolutionary history of plants
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18.3 Plants have an alternation of generations life cycle
Alternation of Generations A sporophyte represents the diploid generation
and a gametophyte represents the haploid generation Sporophyte (2n) produces spores by meiosis
A spore is a haploid reproductive cell that develops into a new organism without needing to fuse with another reproductive cell
A spore undergoes mitosis to become a gametophyte Gametophyte (n) produces gametes
In plants, eggs and sperm are produced by mitosis A sperm and egg fuse, forming a diploid zygote that
undergoes mitosis and becomes the sporophyte
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Figure 18.3 Alternation of generations
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18.4 Sporophyte dominance was adaptive to a dry land environment Reproductive Adaptation to the Land Environment Sporophyte dominance can be associated with an increasing
adaptation for reproduction in a dry, terrestrial environment Ferns are seedless vascular plants with a dominant sporophyte
The sporophyte produces spores that disperse (scatter) separate gametophytes
The gametophyte is a small, heart-shaped structure that has no vascular tissue and can dry out if the environment is not moist
Each archegonium on the surface of a gametophyte produces an egg that is fertilized by a flagellated sperm, which must swim to the archegonium in a film of external water
Other Adaptations to the Land Environment Cuticle - relatively impermeable layer and provides an effective barrier
to water loss, but it also limits gas exchange Leaves have little openings called stomata (sing., stoma) that let carbon
dioxide enter while allowing oxygen and water to exit 18-11
Figure 18.4A Reduction in the size of the gametophyte as sporophyte becomes dominant
18-12
Flowering plants are seed plantswith a dominant sporophyte
In flowering plants: Sporophyte produces seeds that disperse separate
sporophytes protected by seed coats Female gametophyte is microscopic and retained and
protected within an ovule, a structure located within the tissue of a flower
The male gametophytes are pollen grains that are transported by wind, insects, or birds They do not need external water to reach the egg
18-13
Figure 18.4B Protection of eggs and embryos
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Figure 18.4C Features of the leaves of vascular plants
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Plants Are Adapted to the Land Environment
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18.5 Bryophytes are nonvascular plants in which the
gametophyte is dominant Nonvascular plants lack a specialized means of
transporting water and organic nutrients They do not have true roots, stems, and leaves
bryophyte (lowercase b) - general term for nonvascular plants
The Generations of Bryophytes Gametophyte is the dominant generation Female gametophyte produces eggs in archegonia, and the male
gametophyte produces flagellated sperm in antheridia Sperm swim to the vicinity of the egg in a continuous film of water Zygote becomes a sporophyte embryo that is protected from
drying out within the archegonium The lack of vascular tissue and the need for sperm to
swim to archegonia in a film of water largely account for the limited their height 18-17
Figure 18.5A Representative bryophytes
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Figure 18.5B Moss life cycle, Polytrichum sp
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18.6 Ferns and their allies have a dominant vascular sporophyte
Today’s seedless vascular plants Club mosses, horsetails and ferns
Ferns (phylum Pterophyta) include approximately 11,000 species Ferns are most abundant in warm, moist, tropical regions, but
can also be found in temperate regions Range in size from less than 1 cm to giant tropical tree ferns that
exceed 20 m Large leaves of ferns, called fronds, are commonly divided into
leaflets
Economic Value of Ferns Often used by florists in decorative bouquets and as ornamental
plants in the home and garden18-20
Figure 18.6A Sporophyte of a club moss
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Figure 18.6B Diversity of fern fronds
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Figure 18.6C Fern life cycle
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18.7 Most gymnosperms bear coneson which the seeds are “naked”
Diversity of Gymnosperms Four groups of living gymnosperms: cycads,
ginkgoes, gnetophytes, and conifers All of these plants have ovules and subsequently
develop seeds that are exposed on the surface of cone scales or analogous structures
Conifers (phylum Coniferophyta) Consist of about 575 species of trees
Many are evergreens such as pines, spruces, firs, cedars and hemlocks
Economic Value of Conifers Wood of conifers is used extensively in construction
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Figure 18.7A Gymnosperm diversity
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Figure 18.7B Pine life cycle
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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES
18.8 Carboniferous forests became the coal we use today
Our industrial society runs on fossil fuels, such as coal
During Carboniferous period (>300 MYA) a great swamp forest encompassed much of Northern Hemisphere Enormous amount of biomass Didn’t decay when trees fell in the water Remains became covered by sediment that changed
to sedimentary rock With pressure, and the organic material became coal
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Figure 18.8 Swamp forest of the Carboniferous period
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18.9 Angiosperms are the flowering plants
Angiosperms (phylum Anthophyta) 240,000 known species Evolved at beginning of the Cenozoic era (65 MYA) when the first
flying insects appeared Flower and their pollinators evolved together
Flower involved in pollination Fruit serves as a means of seed dispersal
Angiosperm Diversity Monocotyledones (or monocots)
about 65,000 species Eudicotyledones (or eudicots)
about 175,000 species
Cotyledons - seed leaves with nutrients that nourish the embryo
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Figure 18.9 Generalized flower
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18.10 The flowers of angiosperms produce “covered” seeds
Fruits Fruits of flowers protect and aid in seed dispersal
Seeds are transported by wind, gravity, water, or animals to another location
Fleshy fruits may be eaten by animals, which transport the seeds to a new location and then deposit them when they defecate
Flowers and Diversification Today there are 240,000 species of flowering plants
and 700,000 species of insects Suggests that success of angiosperms has
contributed to the success of insects, and vice versa18-31
Figure 18.10 Flowering plant life cycle
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Figure 18.10 Flowering plant life cycle (continued)
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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES
18.11 Flowering plants provide many services
Humans derive most of their sustenance from three flowering plants Wheat
First cultivated in the Middle East about 8000 B.C. thought to be one of the earliest cultivated plants
Corn Properly called maize, first cultivated in Central America about 7,000
years ago Rice
Originated several thousand years ago in southeastern Asia, where it grew in swamps
Used for centuries for many important items Lumber - major part of buildings (mainly comes from conifers) Rubber - first made from the thick sap (latex) of the rubber tree About 50% of all pharmaceuticals come from plants
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Figure 18.11A Some species of grain
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Figure 18.11B Uses of plants
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Fungi Have Their Own Evolutionary History
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18.12 Fungi differ from plants and animals
Fungi (domain Eukarya, kingdom Fungi) Structurally diverse group of eukaryotes
Strict heterotrophs that release digestive enzymes into the external environment and digest their food outside the body
Mycelium - fungus body, a mass of filaments called hyphae
Fungal cells are different from plant cells Lack chloroplasts and their cell wall contains chitin rather
than cellulose Fungi are adapted to life on land by producing
windblown spores during both asexual and sexual reproduction
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Figure 18.12A Fungal mycelia and hyphae
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18.13 Fungi have mutualistic relationships with algae and plants
In a mutualistic relationship, two different species live together and help each other out Lichen - a mutualistic association between a
particular fungus and a cyanobacteria or green algae Three varieties
Compact crustose lichens seen on bare rock Shrublike fruticose lichens Leaflike foliose lichens
Mycorrhizal fungi form mutualistic relationships with the roots of most plants Helps plants grow more successfully in dry or poor soils
particularly those deficient in inorganic nutrients18-40
18.14 Fungi occur in three main groups
Zygospore Fungi (phylum Zygomycota) Mainly saprotrophs, but some parasitize small protists,
worms, and even insects
Sac Fungi (phylum Ascomycota) Nearly 75% of all described fungal species Yeasts - unicellular forms mainly in Ascomycota
Club Fungi (phylum Basidiomycota) Name comes from the reproductive structure, the
basidium (pl., basidia) The basidia are located within a basidiocarp
When you eat a mushroom, you are eating a basidiocarp18-41
Figure 18.14A Black bread mold, Rhizopus stolonifer
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Figure 18.14B Sexual reproduction in sac fungi
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Figure 18.14C Asexual reproductive structures in sac fungi
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Figure 18.14D Sexual reproduction in club fungi involves a basidiocarp of which three types are shown
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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES
18.15 Fungi have economic and medical importance
Economic Importance Help produce medicines and many foods
Mold Penicillium was original source of penicillin
In U.S., 1.13 billion pounds of mushrooms consumed annually
Fungal pathogens are a major concern for farmers
Medical Importance Mycoses are diseases caused by fungi Tineas are infections of the skin caused by fungi
Ringworm is a cutaneous infection contracted from soil Athlete’s foot is a tinea that affects the skin between the toes
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Connecting the Concepts:Chapter 18
Both plants and fungi are multicellular organisms adapted to living on land Four plant adaptations to a dry environment
Protect the sporophyte embryo from drying out Vascular tissue transports water and solutes Seeds allow the sporophyte to be dispersed Flowers get animals to pollinate and disperse seeds
Fungi are adapted to the land environment Produce windblown spores for asexual and sexual life cycles Saprotrophic and release enzymes into the environment to digest
organic remains and absorb nutrients
Without photosynthesis from algae and plants and decomposition from bacteria and fungi, animals could not exist Animals are not essential to the biosphere, but plants and fungi
are18-47